1. Field of the Invention
The present invention relates to a lighting device for use in a laser system or a liquid crystal display.
2. Description of the Related Art
A conventional lighting device typically includes a light source and a light reflective cylinder and is adapted for use in a slab laser system, a liquid crystal display, and advertising or other signs.
In the prior art lighting device for use, for example, in a slab laser system, a light reflective cylinder has a semicircular, elliptical or flat surface. FIG. 6 is a sectional view of a conventional lighting device designed to actuate a slab laser system. The lighting device has a housing C within which a cylindrical Xe flash lamp or a linear source of light 2 extends in a direction normal to the surface of the drawing figure. The housing C is made of brass and has an inner surface machined to a cylindrical shape, then abraded, and plated with gold to provide a mirror surface. The housing C has a inner light reflective cylinder 3.
The housing C has an open end. A slab laser element 1, Nd:Yag, has a width W and is held in place by a Teflon thermal insulant 4 which is, in turn, fixed to the open end of the housing C. The slab laser element 1 is spaced a distance h away from the light source 2 and actuated by light from the light source 2.
FIG. 5 shows the relationship between the light source and the light intensity on the light receiving surface. In the prior art lighting device shown in FIG. 6, the origin is located on the slab laser element 1 at a point right below the light source 2. The intensity D(X) of direct light from the light source 2 onto the light receiving surface 1 at coordinates (X, 0) is represented as follows: ##EQU1## where I is the light intensity of the light source 2, and Rd is reflectance of the light receiving surface 1.
From the equation (1), it is clear that in the prior art lighting device of FIG. 6, the intensity of direct light from the light source 2 onto the light receiving surface 1 decreases as the value of X increases. Although additional light or reflected light from the light reflective cylinder 3 exists, it is clear that the intensity of the reflected light is the same as that of the direct light since the light reflective cylinder has a cylindrical surface.
FIG. 4 shows the characteristic of light intensity on the light receiving surface. In the prior art lighting device shown in FIG. 6, a curve A of FIG. 4 shows the intensity of direct light from the light source 2. A curve B shows the intensity of direct light from the light source 2 plus reflected light from the light reflective cylinder 3.
In the prior art lighting device, the intensity of light on the light receiving surface is maximum at a point right below the light source 2. The intensity of light decreases as the distance between the light source 2 and the light receiving surface increases. Accordingly, the intensity of light directed onto the light receiving surface is not constant.